Impulse event separating apparatus and method

ABSTRACT

An impulse event separating method, and an apparatus to perform the method, the method including dividing an input signal into frame units and dividing each frame into a plurality of frequency sub-bands; obtaining a power variation and phase variation of the signal of each of the frequency sub-bands, and detecting a plurality of local onsets using the power variation and the phase variation; obtaining a global onset from the local onsets and triggering a plurality of event components using the local onsets and the global onset; tracking and combining the event components in each of the frequency sub-bands to form events; and determining whether the events comprise an impulse event with reference to an impulse event property.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of Korean Patent ApplicationNo.10-2004-0091451, filed on Nov. 10, 2004, in the Korean IntellectualProperty Office, the disclosure of which is incorporated herein byreference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an impulse event separating apparatusand method, and, more particularly, to a method of separating an impulseevent from a successive sound, and an apparatus to perform the method.

2. Description of the Related Art

An impulse event, that is, an impact sound, is generated by mechanicalinteraction between objects, and has a short duration and a highintensity. The impact sound occurs suddenly in background sounds whichare relatively stable and can be estimated. According to signalprocessing theory, the impact sound can be modeled into a zero-stateimpulse response of a linear system.

Examples of impact sounds include a simplex sound, such as the soundmade by striking glass with a rod, and a complex sound, such as anexplosive sound or the sound made when a coin falls to the floor.

The impact sound generally has an onset stage and an attenuating stage.In the onset stage, the physical event making the impact sound has ashort duration and a high intensity. If the onset is detected, the startof the impact sound can be determined.

Generally, an ideal impulse signal is linearly attenuated in theattenuating stage. That is, the energy of a log function substantiallyhas a linear attenuation slope. According to this property, the eventcan be tracked, and the energy distribution of the impact sound can becalculated.

Since the successive sounds in which the impact sound and the non-impactsound are mixed generally share frequency bands and overlap each otherin the time domain, the impact sound must be distinguished from thesesuccessive sounds.

Conventional techniques for separating the impact sound include U.S.Pat. No. 6,249,749, U.S. Pat. No. 6,182,018 and U.S. Pat. No. 5,831,936.

SUMMARY OF THE INVENTION

The present invention provides an impulse event separating method, andan apparatus to perform the method, of detecting an onset from an inputaudio signal in each frequency band, detecting an event using the onset,and determining whether the event is an impulse event.

Additional aspects and/or advantages of the invention will be set forthin part in the description which follows and, in part, will be apparentfrom the description, or may be learned by practice of the invention.

According to an aspect of the present invention, there is provided animpulse event separating apparatus comprising a preprocessing unit whichdivides an input signal into frame units; an event detecting unit whichdivides the frame into a plurality of frequency sub-bands, obtains powervariations and phase variations of the signals of each of the sub-bandsto detect a plurality of onsets, and detects a plurality of events usingthe detected onsets; an event buffer which stores the detected events;and an impulse event determining unit which determines whether thedetected events comprise an impulse event with reference to an impulseevent property.

According to another aspect of the present invention, there is providedan impulse event separating method comprising dividing an input signalinto frame units and dividing each frame into a plurality of frequencysub-bands; obtaining a power variation and phase variation of the signalof each of the frequency sub-bands, and detecting a plurality of localonsets using the power variation and the phase variation; obtaining aglobal onset from the local onsets and triggering a plurality of eventcomponents using the local onsets and the global onset; tracking andcombining the event components in each of the frequency sub-bands toform events; and determining whether the events comprise an impulseevent with reference to an impulse event property.

BRIEF DESCRIPTION OF THE DRAWINGS

These and/or other aspects and advantages of the invention will becomeapparent and more readily appreciated from the following description ofthe embodiments, taken in conjunction with the accompanying drawings ofwhich:

FIG. 1 is a block diagram illustrating an impulse event separatingapparatus according to an embodiment of the present invention;

FIG. 2 is a block diagram illustrating an event detecting unit shown inFIG. 1;

FIG. 3 is a block diagram illustrating a scout shown in FIG. 2;

FIG. 4 is a block diagram illustrating a local onset detecting unitshown in FIG. 3;

FIG. 5 defines an external and internal domain so as to combine aplurality of local onsets;

FIG. 6 illustrates an example of tracking ECs by a frequency sub-band;and

FIGS. 7A through 7D illustrate the result of approximating a log powersignal of an input signal.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Reference will now be made in detail to the embodiments of the presentinvention, examples of which are illustrated in the accompanyingdrawings, wherein like reference numerals refer to the like elementsthroughout. The embodiments are described below to explain the presentinvention by referring to the figures.

FIG. 1 is a block diagram illustrating an impulse event separatingapparatus according to an embodiment of the present invention. Theimpulse event separating apparatus includes a preprocessing unit 10, anevent detecting unit 11, an event buffer 12, and an impulse eventdetermining unit 13.

The preprocessing unit 10 divides an input audio signal into frameunits, extracts a frequency band corresponding to an impulse event fromeach frame, and samples and converts the frequency band into a digitalsignal.

The event detecting unit 11 detects an event from the digital signal,and the event buffer 12 buffers the event detected in the eventdetecting unit 11. The impulse event determining unit 13 determineswhether the event stored in the event buffer 12 is an impulse event, andseparates the impulse event therefrom.

FIG. 2 is a block diagram of the event detecting unit 11 in FIG. 1. Theevent detecting unit 11 includes a controlling unit 20, a plurality ofscouts 21 a, 21 b, . . . 21 k, a plurality of event component (EC) pools22 a, 22 b, . . . 22 k, and an event forming unit 23.

The controlling unit 20 divides a frame output from the preprocessingunit 10 into a plurality of sub-bands and outputs them to the scouts 21a, 21 b . . . 21 k. The scouts 21 a, 21 b, . . . 21 k detect localonsets from the corresponding sub-bands and output the local onsets tothe controlling unit 20. At this time, the controlling unit 20 combinesthe local onsets detected in the scouts 21 a, 21 b, . . . 21 k to form aglobal onset, and feeds the global onset back to the scouts 21 a, 21 b .. . 21 k.

Here, each sub-band may be uniformly divided from the frequency band ofthe corresponding frame, and may be divided according to the output of acochlear filter. The impulse response of the cochlear filter can beapproximated through a Gammatone filter function expressed by Equation1.g(t)=t ^(n-1) exp(−2πbt)cos(2πf ₀ t+φ)   (1)Wherein f₀ is the center frequency of the cochlear filter, n is adegree, φ is a phase difference, and b is a constant.

The controlling unit 20 may include a cochlear filter bank having theimpulse response as shown by Equation 1 for the center frequency of eachsub-band, and can provide the output thereof to each of the scouts 21 a,21 b . . . 21 k. The controlling unit 20 may further include asynchronizing unit so as to simultaneously drive the scouts 21 a, 21 b,. . . 21 k.

The EC pools 22 a, 22 b, . . . 22 k include a plurality of ECs which aretriggered using the local onsets detected in the scouts 21 a, 21 b, . .. 21 k. Each EC is triggered in response to the power suddenly beingincreased in the corresponding sub-band, and is stopped in response tothe power falling below a zero event component level. Here, the zeroevent component level refers to the power of an acoustical backgroundwhich exists when no EC exists in the corresponding sub-band.

The event forming unit 23 combines the ECs triggered in the EC pools 22a, 22 b, . . . 22 k to form the event. Also, the event forming unit 23subtracts the event from the signal output from the preprocessing unit10 and outputs a zero event, that is, a whole background sound.

FIG. 3 is a detailed block diagram illustrating one of the scouts 21 a,21 b, . . . 21 k in FIG. 2. The scout includes a local onset detectingunit 30, a local estimating unit 31, and a trigger unit 32. The impulseevent starts at the onset. That is, the ECs of the EC pools 22 a, 22 b,. . . 22 k start at the onset. Accordingly, by detecting every onset,the start of every event can be detected.

The local onset detecting unit 30 detects the local onset from anamplitude spectrum and a phase spectrum of the signal input from thecontrolling unit 20. FIG. 4 is a detailed block diagram of the localonset detecting unit 30. The local onset detecting unit 30 includes aninstant power measuring unit 40, a delta power calculating unit 41, alog power measuring unit 42, a delta log power calculating unit 43, aphase span unit 44, a matched filter 45, an onset filter unit 46, and amultiplier 47.

If the amplitude spectrum of the input signal of the frame (t) is{Y(t,1), Λ, Y(t, N)}, the instant power measuring unit 40, the deltapower calculating unit 41, the log power measuring unit 42, and thedelta log power calculating unit 43 can respectively obtain the power,the delta power, the log power, and the delta log power, expressed byEquation 2, from the amplitude spectrum. $\begin{matrix}{{{{Power}(t)} = {\frac{1}{N}{\sum\limits_{n = 1}^{N}\quad{{Y\left( {t,n} \right)}}^{2}}}}{{{DPower}(t)} = {{{Power}(t)} - {{Power}\left( {t - 1} \right)}}}{{{LogPower}(t)} = {\log\left( {\frac{1}{N}{\sum\limits_{n = 1}^{N}\quad{{Y\left( {t,n} \right)}}^{2}}} \right)}}{{{DLogPower}(t)} = {{{LogPower}(t)} - {{LogPower}\left( {t - 1} \right)}}}} & (2)\end{matrix}$Wherein power(t) is the instant power, DPower(t) is the delta power,Logpower(t) is the log power, and DlogPower(t) is the delta log power.

The instant power and the log power represent the trace of the absolutevalue of the energy, and the delta power and the delta log power includethe variation of the energy between frames. These values increaserapidly in the onset, with the delta log power increasing particularlyrapidly.

The phase span unit 43 measures the phase variation of the linear phasecomponent in the sub-band frequency domain. According to the Fourieranalysis theory, the signal is expressed by the amplitude spectrum andthe phase spectrum. The amplitude encodes the frequency content of thesignal, and the phase represents a temporal or spatial structure.Accordingly, the temporal location of the onset can be expressed by theslope of the linear phase component. If an unwrapped phase spectrumadjacent to the frame (t) is {φ(t,0), . . . , φ(t, N/2)}, the unwrappedphase spectrum can be approximated by the linear function as shown byEquation 3.{circumflex over (φ)}(t,n)=α(t)·n+{circumflex over (φ)}( t,0), n=0, . .. , N/2   (3)Wherein α(t) is the slope of the linear phase component.

According to Equation 3, the phase span of the frame (t) is calculatedby Equation 4.PhaseSpan(t)=α(t)N/2≅φ(t,N/2)−φ(t,0)   (4)

Since the general phase span of the onset is linear, it can be expressedby Equation 5. $\begin{matrix}{{p(n)} = \left\{ \begin{matrix}{{n\quad\pi},} & {0 \leq n < {N/2}} \\{0,} & {otherwise}\end{matrix} \right.} & (5)\end{matrix}$

Since the matched filter 44 is used for matching the pattern, it has theimpulse response expressed by Equation 6. $\begin{matrix}{{h_{mf}(t)} = \left\{ \begin{matrix}{{c\quad{\pi\left( {{N/2} - t} \right)}},} & {0 \leq t < {N/2}} \\{0,} & {otherwise}\end{matrix} \right.} & (6)\end{matrix}$

The output of the matched filter for the phase span result of Equation 5is expressed by the conjugate of Equations 5 and 6 as shown by Equation7. $\begin{matrix}{{{FilteredPhaseSpan}(t)} = {\frac{cN}{2}{\sum\limits_{n = 0}^{{N/2} - 1}\quad{\left( {\frac{N}{2} - n} \right)\pi\quad{\alpha\left( {t - n} \right)}}}}} & (7)\end{matrix}$Wherein c is a constant.

The constant (c) has a value of c=24/(N-2)(N-1)/Nπ², so that the maximumof the result of Equation 7 becomes 1.

The onset filter unit 46 emphasizes the variation degree of the inputsignal, and includes a plurality of secondary filters to which primaryfilters having a delay-add filter shape are connected. The onset filtersrespectively filter the outputs of the instant power measuring unit 40,the delta power calculating unit 41, the log power calculating unit 42,and the delta log power calculating unit 43. Each onset filter has theimpulse response expressed by Equation 8.h _(of)(t)=Ae ^(t/T) ¹ −Be ^(t/T) ²   (8)Wherein A=1−e ^(−1/T) ¹ , B=1−e ^(−1/T) ² , and T ₁ <T ₂

The onset filter having the impulse response shown by Equation 8 issensitive to the input which varies relatively rapidly.

The multiplier 47 multiplies a plurality of filter outputs of the onsetfilter unit 46 by the output of the matched filter 45 to output thelocal onset for the corresponding sub-band.

The controlling unit 20 detects the global onset from the plurality oflocal onsets detected by the scouts 21 a, 21 b, . . . 21 k. FIG. 5defines an external and internal domain so as to combine the pluralityof local onsets.

Referring to FIG. 5, f(t) represents the output of the onset filterwhich is applied to the output of the log power calculating unit 42. Thepoints t₀ and t₃ represent the zero points of f(t) closed to the mainpeak, and t₁ and t₂ represent the zero points of f(t)-z closed to themain peak. Here, z is a constant which is selected experimentally. Thesection (t₀, t₃) is defined as the external domain, and the section (t₁,t₂) is defined as the internal domain. The controlling unit 20 combinestwo local onsets to make one global onset when the external domain ofone local onset overlaps with the internal domain of the other localonset.

If the global onset is made, the controlling unit 20 sends notice thatthe global onset is made to the local estimating unit 31 of the scoutwhich does not detect the local onset. The local estimating unit 31receives the notice and detects the power of the corresponding sub-bandat the global onset time. If the power is greater than an estimate, anotice trigger EC is triggered by the trigger unit 32. The localestimating unit 31 estimates the recent power before the global onsettime.

The trigger unit 32 triggers the EC according to the notice output fromthe local estimating unit 31 or the local onset output from the localonset detecting unit 30.

The EC pools 22 a, 22 b, . . . 22 k include the plurality of ECstriggered by the trigger unit 32. The duration and the power during theduration of each EC are estimated. Each EC becomes either a maskingstate or a masked state, and one EC of the masking state exists in onesub-band. At this time, any ECs other than the masking EC become themasked state. If a new EC is triggered by the trigger unit 32, itbecomes the masking state.

The EC pools 22 a, 22 b, . . . 22 k also include a zero EC. The zero ECsets a zero event component level for each sub-band and represents theacoustic background in that sub-band. The zero EC becomes the maskingstate if it is the only EC in the sub-band, and otherwise becomes maskedby the other ECs. If the zero EC is in the masking state, the localestimated value rapidly converges to the acoustic background of thecorresponding sub-band. The power of the zero EC is the zero eventcomponent level, and the other ECs disappear when their power fallsbelow the zero event component level. The instant power of the masked ECis estimated in the local estimating unit 31 at the correspondinginstant, and the instant power of the masking EC is the value obtainedby subtracting the sum of the powers of the masked ECs from the totalpower of that frequency band.

The event forming unit 23 tracks the ECs included in the EC pools 22 a,22 b, . . . 22 k and estimates the power of the EC at every instant andthe end point of each EC to obtain the power function of each EC.

FIG. 6 illustrates an example of tracking ECs by a frequency sub-band.FIG. 6(a) illustrates two impulse event components (A, B), and Boverlaps with the middle of A. In FIG. 6(b), the solid line indicatesthe local data of the corresponding sub-band, and the dotted lineindicates the estimated power of each EC. FIG. 6(c) illustrates theresult of the event forming unit 32 separating the data of FIG. 6(a)into three ECs, that is, the zero EC 60, the EC (A) 61, and the EC (B)62. In section 1, the impulse EC does not exist, and thus the zero ECbecomes the masking EC, and the power of the zero EC becomes the zeroevent component level. In section 2, the EC (A) occurs, and the zero ECis masked. In section 3, the EC (B) occurs and becomes the maskingstate, and thus the EC (A) and the zero EC are masked. Since the powerof the EC (B) becomes lower than that of the EC (A) in section 4, the EC(B) disappears. In section 5, the EC (A) becomes the masking EC, untilthe power of the EC (A) becomes lower than the zero event componentlevel at the end of section 5, and thus the EC (A) disappears. Insection 6, the zero EC becomes the masking state again.

Accordingly, the tracking of the event component is accomplishedaccording to the variation of the power of the masking ECs at everyinstant. The event forming unit 23 determines the duration withreference to the start point and the end point of each EC, and forms theevent if the above-mentioned event tracking process is completed. Thatis, referring to FIGS. 6A(a) through 6(c), the time at which the powerof the masking EC becomes greater than the zero event component level isthe start point of the event, and the time at which the power of themasking EC becomes less than the zero event component level is the endpoint of the event.

The event buffer 12 temporarily stores the events formed in the eventforming unit 23.

The impulse event determining unit 13 determines whether the eventsstored in the event buffer 12 are impulse events or not, with referenceto a common property of the impulse events.

In order to identify impulse events, two examining processes are needed.Between them, it is determined whether the power of the detected onsetincreases rapidly. This is performed in the local onset detecting unit30, which searches the start point of as many of the impulse events aspossible. However, three tests are used to identify impulse events in agiven time period [a, b]. First, whether the instant power function ofthe signal between the onset and the power peak point reaches asufficiently large value at time (b); second, whether the instant powerfunction has largely increased during the time period [a, b]; and third,whether the time period [a, b] is sufficiently small.

Here, determining whether the instant power function has largelyincreased must satisfy the following requirement for damped oscillation.

The log power of the section during which the signal is attenuated issubstantially linear from the peak to a noise level. This pattern isequal to the attenuation pattern of the single mode damped oscillation.The attenuation pattern of the damped oscillation can be expressed byEquation 9. $\begin{matrix}{{\frac{\mathbb{d}\left( {{LogPower}(t)} \right)}{\mathbb{d}t} < 0},{\frac{\mathbb{d}^{2}\left( {{LogPower}(t)} \right)}{\mathbb{d}\quad t^{2}} = 0}} & (9)\end{matrix}$

If the power peak time is t_(p), the noise level is n1, and the timewhen the power falls below the noise level is t_(e), then using theseparameters, the inequality of Equation 9 can be quantitated using thepower function expressed by Equation 10.z(t)=c(1 31 t)^(λ)  (10)

Here, c is a constant determined by z(t_(p))=Power(t_(p)) andz(t_(e))=Power(t_(e)), λ is a value for representing the impulsivenessof the sound, and z(t) is the instant power.

The function of Equation 10 satisfies the inequality of Equation 9 whenλ is a value between 0 and 1. If λ>>1, it is difficult to be consideredas an impulse event. An ideal λ approaches 1, and most impulse eventsare not greater than 3.

FIGS. 7A through 7D illustrate the result of approximating a log powersignal of an input signal according to Equation 10. Reference numerals90-1, 90-2, 90-3, and 90-4 indicate original signals, and 91-1, 91-2,91-3, and 91-4 respectively illustrate the log powers of the originalsignals. 92-1, 92-2, 92-3, and 92-4 illustrate the results ofapproximating the log power signals. It is noted that the approximatedlog power signal 0 for the corresponding log power between the noiselevel set to each signal and a threshold value higher than the noiselevel and λ is approximated to 0.520, 0.959, 1.435, and 37.59 for thelog power which is attenuated from the onset to the threshold value.FIG. 7B illustrates an ideal impulse event in which λ approaches 1.FIGS. 7A and 7C illustrate the impulse events. In FIG. 7D, the powerlevel increases rapidly. However, FIG. 7D is difficult to be consideredas an impulse event, because λ>>1. Actually, FIG. 7D illustrates aspeech signal, not an impulse event.

The invention can also be embodied as computer readable code on acomputer readable recording medium. The computer readable recordingmedium is any data storage device that can store data which can bethereafter read by a computer system. Examples of the computer readablerecording medium include read-only memory (ROM), random-access memory(RAM), CD-ROMs, magnetic tapes, floppy disks, optical data storagedevices, and carrier waves (such as data transmission through theinternet). The computer readable recording medium can also bedistributed over network coupled computer systems so that the computerreadable code is stored and executed in a distributed fashion. Also,functional programs, code, and code segments for accomplishing thepresent invention can be easily construed by programmers skilled in theart to which the present invention pertains.

According to the present invention, an impulse event can be separated byseparating the successive audio stream into frequency bands to detectlocal onsets, forming the events using the detected onsets, andexamining the log powers of the events. Since the present inventiondetermines an impulse event, for example, a glass-breaking sound, agunshot, or footsteps, from the sound generated in surroundings, it canbe applied to a security system and can diagnose a defect of a structurethrough acoustic diagnosis.

Although a few embodiments of the present invention have been shown anddescribed, it would be appreciated by those skilled in the art thatchanges may be made in these embodiments without departing from theprinciples and spirit of the invention, the scope of which is defined inthe claims and their equivalents.

1. An impulse event separating apparatus, comprising: a preprocessingunit which divides an input signal into frame units; an event detectingunit which divides each frame into a plurality of frequency sub-bands,obtains power variations and phase variations of the signals of each ofthe sub-bands to detect a plurality of onsets, and detects a pluralityof events using the detected onsets; an event buffer which stores thedetected events; and an impulse event determining unit which determineswhether the detected events comprise an impulse event with reference toan impulse event property.
 2. The apparatus according to claim 1,wherein the event detecting unit comprises: a controlling unit whichdivides the frame into the frequency sub-bands and detects a globalonset from local onsets; a plurality of scouts which respectively detectthe local-onsets using the power variations and the phase variations ofthe signals of the frequency sub-bands, trigger a first type of eventcomponents, output the local onsets to the controlling unit, and triggera second type of event components; an event component pool comprisingthe first and second types of event components triggered by each of thescouts; and an event forming unit which tracks and combines the eventcomponents to form the detected events.
 3. The apparatus according toclaim 2, wherein the controlling unit uniformly divides the frame intothe frequency sub-bands.
 4. The apparatus according to claim 2, whereinthe controlling unit comprises a plurality of cochlear filters havingimpulse responses which are approximated by a Gammatone function.
 5. Theapparatus according to claim 2, wherein each of the scouts comprises: alocal onset detecting unit which detects the local onset using the powervariation and the phase variation of the signal of the frequencysub-band; a local estimating unit which measures a power of the signalof the frequency sub-band at the time that the global onset is detected;and a trigger unit which triggers the first type of event component bythe local onset, and triggers the second type of event component inresponse to the power measured in the local estimating unit beinggreater than a predetermined estimated value.
 6. The apparatus accordingto claim 5, wherein the local onset detecting unit comprises: a powervariation detecting unit which detects the power and the power variationof the signal of the frequency sub-band; a phase variation detectingunit which detects the phase variation of the signal of the frequencysub-band; and a multiplier which multiplies the power variation by thephase variation to output the local onset.
 7. The apparatus according toclaim 6, wherein the power variation detecting unit comprises: aninstant power measuring unit which measures the power of the signal ofthe frequency sub-band; a delta power calculating unit which calculatesa variation from a the power of the previous frame using the measuredpower; a log power measuring unit which measures a log power obtained bytaking a log of the signal of the frequency sub-band; a delta log powercalculating unit which calculates a variation of a log power of theprevious frame using the log power; and an onset filter unit whichfilters the power, the power variation, the log power, and the variationof the log power to emphasize the variation degree.
 8. The apparatusaccording to claim 7, wherein the onset filter unit comprises asecondary filter having an impulse response expressed by the equationh _(of)(t)=Ae ^(t/T) ¹ −Be ^(t/T) ² , for the power, the powervariation, the log power, and the variation of the log power,wherein A=1−e ^(−1/T) ¹ , B=1−e ^(−1/T) ² and T <T ₂.
 9. The apparatusaccording to claim 6, wherein the phase variation detecting unitcomprises: a phase span unit which approximates the phase of the signalof the frequency sub-band by a linear function and detects the variationdegree of the approximated phase; and a matched filter which matches apattern of the detected phase variation.
 10. The apparatus according toclaim 2, wherein if a domain between zero points on the basis of a mainpeak in a curve representing the power of the signal of the frequencysub-band output from the scout is defined as an external domain, and adomain between zero points in a curve adjusted by a predetermined valuefrom the curve is defined as an internal domain, the controlling unitdetects the global onset by combining two local onsets to make oneglobal onset in response to the external domain of one local onsetoverlapping with the internal domain of the other local onset.
 11. Theapparatus according to claim 1, wherein the impulse event determiningunit determines whether the events comprise an impulse event based on apower increment degree and a power attenuation pattern during apredetermined time period of the impulse event.
 12. The apparatusaccording to claim 11, wherein the power attenuation pattern isdetermined such that when the power z(t) of the signal of the frequencysub-band is expressed by the equationz(t)=c(1−t)^(λ), λ satisfies a predetermined condition, wherein t_(p) isthe power peak time of the signal of the frequency sub-band, t_(e) isthe time that the power of the signal of the frequency sub-band fallsbelow a noise level, c is a constant determined by z(t_(p))=Power(t_(p))and z(t_(e))=Power(t_(e)) and λ is a value for determining whether thesound is an impulse event.
 13. An impulse event separating method,comprising: dividing an input signal into frame units and dividing eachframe into a plurality of frequency sub-bands; obtaining a powervariation and phase variation of the signal of each of the frequencysub-bands, and detecting a plurality of local onsets using the powervariation and the phase variation; obtaining a global onset from thelocal onsets and triggering a plurality of event components using thelocal onsets and the global onset; tracking and combining the eventcomponents in each of the frequency sub-bands to form events; anddetermining whether the events comprise an impulse event with referenceto an impulse event property.
 14. The method according to claim 13,wherein the dividing each frame comprises uniformly dividing the frameinto the frequency sub-bands.
 15. The method according to claim 13,wherein the dividing each frame comprises dividing the frame using aplurality of cochlear filters having impulse responses which areapproximated by a Gammatone function.
 16. The method according to claim13, wherein obtaining the power variation of the signal of each sub-bandcomprises: obtaining a log power by taking a log of the signal of thesub-band and a power of the signal of the sub-band; obtaining avariation of the signal of the sub-band for a previous frame and avariation of the log power of the signal of the sub-band for theprevious frame; and filtering the power, the power variation, the logpower, and the variation of the log power to emphasize the variationdegree.
 17. The method according to claim 16, wherein filtering thepower, the power variation, the log power and the variation of the logpower is accomplished by a secondary filter having the impulse responseexpressed by the equationh _(of)(t)=Ae ^(t/T) ¹ −Be ^(t/T) ² , for the power, the powervariation, the log power, and the variation of the log power,wherein A=1−e ^(−1/T) ¹ , B=1−e ^(−1/T) ² and T ₁ <T ₂.
 18. The methodaccording to claim 13, wherein obtaining the phase variation comprises:approximating the phase of the signal of the frequency sub-band by alinear function and detecting the variation of the approximated phase;and matched-filtering the measured phase variation.
 19. The methodaccording to claim 13, wherein obtaining the global onset comprises:defining a domain between zero points on a basis of a main peak in acurve representing the power of the signal of the frequency sub-bandoutput from the scout as an external domain, and a domain between zeropoints in a curve adjusted by a predetermined value from the curve as aninternal domain; and combining two local onsets to make one global onsetin response to the external domain of one local onset overlapping withthe internal domain of the other local onset.
 20. The method accordingto claim 13, wherein the tracking of the event components isaccomplished according to the variations of the powers of the eventcomponents which become a masking state in response to the eventcomponents being masking states or masked states according to the powersof the event components.
 21. The method according to claim 20, whereinforming the events is accomplished by detecting the time between thepower of the masking event component becoming greater than apredetermined level and the power of the masking event componentbecoming less than a predetermined level, and setting this as theduration of the events.
 22. The method according to claim 13, whereinthe determining the events comprises determining whether the events arean impulse event based on a power increment degree and a powerattenuation pattern during a predetermined time period of the impulseevent.
 23. The apparatus according to claim 22, wherein the powerattenuation pattern is determined such that when the power z(t) of thesignal of the frequency sub-band is expressed by the equationz(t)=c(1−t)^(λ), λ satisfies predetermined condition, wherein t is thepower peak time of the signal of the frequency sub-band, t is the timethat the power of the signal of the frequency sub-band falls below anoise level, c is a constant determined by z(t_(p))=Power(t_(p)) andz(t_(e))=Power(t_(e)), and λ is a value for determining whether thesound is an impulse event.
 24. A computer-readable medium havingembodied thereon a computer program for an impulse event separatingmethod comprising: dividing an input signal into frame units anddividing each frame into a plurality of frequency sub-bands; obtaining apower variation and phase variation of the signal of each of thefrequency sub-bands and detecting a plurality of local onsets using thepower variation and the phase variation; obtaining a global onset fromthe local onsets and triggering a plurality of event components usingthe local onsets and the global onset; tracking and combining the eventcomponents in each of the frequency sub-bands to form events; anddetermining whether the events comprise an impulse event with referenceto an impulse event property.
 25. A method of separating an impulseevent, the method comprising: detecting a plurality of local onsetsaccording to power variations and phase variations of frequencysub-bands of frames of a signal; obtaining a global onset from the localonsets and triggering a plurality of event components; tracking andcombining the event components to form events; and separating theimpulse event in response to the events comprising the impulse event.26. The method of claim 25, wherein the event components in each of thefrequency sub-bands are combined to form the events.
 27. The method ofclaim 25, further comprising dividing the signal into frames anddividing each of the frames into the frequency sub-bands.
 28. The methodof claim 27, wherein the power and phase variations are determined bycomparing a power and phase of a current frame with a power and phase ofa previous frame.
 29. A method of separating an impulse event, themethod comprising: detecting onsets in frequency sub-bands of a signal;tracking and combining event components from the onsets in the frequencysub-bands to form events; and separating the impulse event from thesignal in response to the events combining to form the impulse event.